Fuel injectors are used to inject fuel into the combustion chambers or intake tracts of internal combustion engines, in particular gasoline or diesel engines. Their purpose is to spray out, within a short available time period, a precisely measured quantity of fuel under high pressure, and to close the injector or nozzle cleanly. The fuel quantity may be varied in an adequately dimensioned quantity range depending on the load and rotation speed, and follows dynamic load changes temporally. The metering of the fuel quantity injected can be predefined in a so-called ballistic injector mode in which the valve assumes an intermediate position between a closed position and a full-stroke injector mode. Another way of predefining the fuel quantity is to predefine the opening time in full-stroke injector mode. At low speeds and loads therefore, very small fuel quantities may be metered and also atomized reliably. Further, fuel may be metered with little noise during the injection process, in order to limit the noise emissions of the engine. Often a so-called choke ring gap is used to meter small fuel quantities. Another approach includes a damper device in the leakage fuel line which, by slowing the outflow of fuel, damps the movement of the needle valve which thus achieves a low opening degree.
DE 3041018 A1 discloses an injector nozzle configuration including a needle valve that may be opened by a high pressure pulse of fuel. A choke valve is fitted in the housing of the injector nozzle between a pressure chamber and a spring chamber. This approach has less delay than the above-mentioned approach, but here the dynamics and precision of fuel quantity control can lead to increased fuel consumption and power losses. In particular, this choke device cannot be controlled in a targeted fashion, and an optimum fuel quantity may not be supplied for all operating load types of the combustion engine.
EP 0240693 B1 discloses an injector nozzle configuration where travel of a needle valve can be limited by an end stop, and a damping stop can be positioned in-between to reduce end stop noise. A pre-injection phase and a main injection phase may be performed, to which a pre-stroke and a main stroke of the valve are allocated, in order to achieve lower combustion noise. In the pre-stroke phase, the fuel pressure need merely overcome the closing force of the return spring. Further, lifting of the needle valve meets an additional resistance from the (lower) fuel pressure behind an additional auxiliary piston which presses on the valve.
WO 94/03720 A1 discloses an approach acting in a similar manner to that described above, and is intended primarily to reduce combustion noise by a pre-stroke valve phase.
Furthermore, to regulate fuel pressure more finely, firstly generally high requirements may be imposed on the actual injection pump control. Therefore, injection systems have also been developed with a common high pressure accumulator, for example known as a common rail. These can be fed with a simpler high pressure pump and the injector phases and quantities are controlled by actuating means, normally electromechanical, which are positioned in each injection nozzle and controlled by a normally electronic controller. Such common rail configurations typically may be fitted with the injector nozzles described above.
However, the inventors herein have identified some potential issues with all of these approaches. For example, in each approach, a dynamic working range (DWR) of the injection nozzle is too small, and the accuracy of the fuel quantity control, particularly in low and high fuel flow phases, may not be suitable. In particular, the above described approaches may not differentiate sufficiently precisely between the control phases of small and large fuel quantities. Such imprecise fuel metering may increase fuel consumption at engine idle speeds, as well as decrease working efficiency in all load situations.
Thus, in one example, some of the above issues may be at least partly addressed by a fuel injector for an internal combustion engine, including a fuel supply channel, a nozzle valve including a valve stem. The nozzle valve and an inner wall of the fuel supply channel may form a first flow cross section and at least one second flow cross section that is larger than the first flow cross section. The fuel injector may further include an actuator to actuate the nozzle valve.
This two stage fuel injector may meter fuel very precisely during low flow operational points by positioning the nozzle valve in a first flow cross section region having a first smaller flow cross section. Further, as fuel flow demand increases, the nozzle valve may be positioned in a second flow cross section region having a second larger flow cross section that is greater than the first flow cross section to achieve flow that meets the demands across the operation range of the engine. In this way, the fuel injector may provide precisely metered fuel during low flow conditions, while meeting peak demand during high flow conditions. In other words, the dynamic flow control range of the fuel injector may be increased relative to prior configurations. Moreover, sufficient differentiation between a low fuel flow and high fuel flow may be realized, and a dependency on viscosity of fuel to provide accurate metering may be reduced.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.